A. A B. B C. A or B D. A and B . It depends if the organism is prokaryotic or eu

Question

A. A B. B C. A or B D. A and B . It depends if the organism is prokaryotic or eukaryotic. 7. You have performed the following mating experiment using Hfr and F- strains of Escherichia coli: Hfr (thr+ leu- strs) x F- (thr- leu- str). Which of the following selective media would you use to grow only recombinant colonies? A) Complete media B) Minimal Media C) Minimal Media + streptomycin D) Minimal Media + leucine E) Minimal Media +streptomycin + leucine 8. All of the following enzymes are involved in DNA replication. Of those listed, which is third in the order? A) DNA helicase 2

Explanation / Answer

Being Hfr the donor E. coli strain and F- is the receptive strain. Therefore the genes of Hfr's genes would be the ones expressing in the recombinant colonies.

thr + : Can synthesize threonine

thr- : Can NOT synthesize threonine

leu - : Can NOT synthesize leucine

strr: resistant to streptomycin

strs: resistant to streptomycin (killed by streptomycin)

Recombinants would be able to grow in a medium without threonine and streptomycin, but with leucine.

Therefore the answer would be D) Minimal media + leucine

Recombination can take place, the question should indicate where between which genes are the sequences that allow recombination, but as it doesn't say anything you can assume that all the genes from Hfr  (thr+ leu- strs) were inserted in the F-'s plasmid chromosome.

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